How do I pass a local variable to a remote `Invoke-Command`?

Question

I'm trying to retrieve the hash of a file located on remote server using Invoke-Command. It works fine when I give the full path as below:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash -Path E:\test\testfile.zip -Algorithm SHA1 
}

But I need to pass the file name via a variable as below:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash -Path "E:\test\$dest.zip" -Algorithm SHA1 
}

How do I access this variable in the scriptblock of a remote session?

Answer 1

In PowerShell 4 (3+ actually) the easiest way is to use the Using scope modifier:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash E:\test\$Using:dest.zip -Algorithm SHA1 
}

For a solution that works with all versions:

Invoke-Command -ComputerName winserver -ScriptBlock {
    param($myDest)

    Get-FileHash E:\test\$myDest.zip -Algorithm SHA1 
} -ArgumentList $dest